The present invention relates to the fabrication of semiconductor integrated circuits (IC's). More particularly, the present invention relates to an improved apparatus and method for etching through a silicon-dioxide containing material, during IC fabrication to create etched features (e.g., trenches, contacts or vias) on the substrate surface.
During the manufacture of a semiconductor-based product, for example, a flat panel display or an integrated circuit, multiple deposition and/or etching steps may be employed. During the deposition step, materials are deposited onto a substrate surface (such as the surface of a glass panel or a wafer). Conversely, etching may be employed to selectively remove materials from predefined areas on the substrate surface. Etching in this manner can create etched features in the dielectric layers of a substrate surface wherein the etched features are filled with metal to form a conductive path.
During etching, a mask formed of a suitable mask material, such as photoresist, is typically employed to define the areas to be etched in the underlying layer. In an exemplary photoresist technique, the photoresist material is first deposited on the underlying layer to be etched. The photoresist material is then patterned by exposing the photoresist material in a suitable lithography system, and by developing the photoresist material to form a mask to facilitate subsequent etching. Using an appropriate etchant, areas of the underlying layer that are unprotected by the mask may then be etched away using an appropriate etchant source gas, thereby forming etched features such as trenches, contacts or vias in the underlying layer.
To facilitate discussion, FIG. 1 depicts an exemplary substrate stack 10, including a mask 12, an underlying layer 14 and a substrate 16. As mentioned, mask 12 may represent photoresist mask or it may be formed of any suitable mask material, including hard mask materials. Underlying layer 14 represents the layer or layers to be etched. For ease of discussion, the underlying layer represents herein a dielectric layer (e.g., a doped or undoped silicon dioxide-containing layer) although, depending on the specific application, the underlying layer may be formed of any etchable material including, for example, organic material. Substrate 16 includes the layers and features that underlie the layer to be etched and may include the semiconductor wafer or the glass panel itself. For the purposes of the invention herein, the composition substrate 16 is somewhat irrelevant.
Within mask 12, there is shown an opening 18, which is created during the mask patterning process. Through opening 18, plasma generated etchants react with the material of underlying layer 14 to etch features (e.g., trenches, contacts or vias) in the underlying layer. During this etching process, the etchants tend to anisotropically etch underlying layer 14 through opening 18 in mask 12, forming an etched feature 20 (e.g., trenches, contacts or vias) having a diameter 22 (or width) and a depth 24. The diameter (or width) is the feature size. The aspect ratio is the ratio of depth over the feature size.
To achieve greater circuit density, modern integrated circuits are scaled with increasingly narrower design rules. As a result, the need for high aspect ratios for features (e.g., trenches, contacts or vias) and substantially straight profiles between devices on the integrated circuit has steadily increased. By way of example, it is not uncommon to employ design rules as small as 0.18 microns or even smaller in the fabrication of some high density integrated circuits. As adjacent devices are packed more closely together, the need for high aspect ratios and straight profiles are increased. The higher aspect ratios allow the feature size (diameter or width) to be smaller thereby allowing closer packing. Additionally, straight profiles ensure that subsequently deposited metal material can properly fill the etched feature, e.g., without suffering voids due to pinch-offs, or the like.
In view of the foregoing, these are desired: improved methods and apparatuses for etching features with high aspect ratios and more vertically etched profiles.